German air raid bunker transformed into renewable energy facility

An imposing concrete flak tower in Hamburg that has sat dormant for decades is now used to generate enough heat for 3,000 homes and enough electricity for another 1,000 via several renewable energy technologies.

Whether it’s a wooden complex of “wellness apartments” or multifamily housing with a slime-fostering façade, it’s always a treat to learn more about the carbon-conscious parade of innovative, unconventional, and often unheimliche buildings to emerge from the Internationale Bauausstellung IBA Hamburg, or as it’s better known, the International Building Exhibition.

Although the IBA Hamburg officially wrapped up in the island district of Wilhelmsburg last year after its seven-year run, notable projects developed as part of the exhibition continue to make the rounds (initial hat tip to Designboom) including this striking green (literal) powerhouse: a hulking, turreted concrete fortress — a Flaktürme, one of two such structures in Hamburg — built by the Nazis in 1943 that’s been transformed by IBA Hamburg and utility company Hamburg Energie into a renewable energy plant complete with an educational visitors area and café. Because really, what would an anti-aircraft bunker conversion be without “hot waffles and refreshing beverages?”

Clad with photovoltaic arrays on its south façade and atop the roof, the nine-story monolithic tower with impenetrable ten-foot-thick walls built to “to demonstrate the supposed valour of the home front” is now capable of producing electricity for as many as 1,000 local homes. But the true pièce de résistance is the building’s 528,000-gallon capacity reservoir “made in a chamber that was the result of internal explosions triggered at the end of the war.” (While the British Army initially wanted to blow the entire building, used as both a shelter for civilians and a line of defense against Allied air strikes, to kingdom come, they opted to just destroy the interior as part of a controlled demolition in 1947).

Acting as a thermal heat store that taps directly into a local heating network, the reservoir itself is heated by a solar thermal array, a woodchip boiler, a combined biomethane heat and power facility, and waste heat generated by Nordische Oelwerke, a nearby industrial plant. All and all, enough heat is generated within the bunker's 60,000-square-foot energy facility to power 3,000 homes when at full capacity.

At the heart of the project is the large heat reservoir built inside the former air raid bunker. In the years to come it will transform the building into an 'Energy Bunker' capable of supplying a district covering an area of more than 1.2 square kilometres (120 hectares), thanks to the integration of different types of environmentally friendly heat and electric power units. The project's most innovative feature is its large-scale buffer storage facility, with an expected total capacity of 2 million litres (2000 cubic metres). This is fed by the heat from a biomethane-fired combined heat and power unit, a wood combustion system, and a solar thermal unit, as well as the waste heat from an industrial plant. The buffering effect of the storage facility will result in a significant drop in the thermal generation performance, from 11 to 6.5 megawatts, enabling the economic use of renewable energy as part of the heat supply concept.

Combined, the Energy Bunker’s electricity- and heat-producing systems boast CO2 savings of about 6,600 metric tons per year. Funded in part by the ERDF (European Regional Development Fund) and the Hamburg Climate Protection Concept, the Energy Bunker cost €27 million to bring to completion over a roughly three-year span (excluding the development stages). A significant portion of those funds were used to rehab and rebuild the interior of the long-abandoned building, which over the decades, had fallen into serious disrepair.

Public access to the facility and it's historic/educational displays cost €1 which includes a voucher for Vju Cafe, a venu that apparently boasts quite thecoffee roasting operation and stunning panoramic views of Hamburg including Wilhelmsburg's PV array- and wind turbine-studded Georgswerder Energy Hill.

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